Bilge pumps, sump pumps and similar DC or AC electric powered pumps used to pump out accumulated water traditionally use a float switch for the pump power circuit in which the water level raises and lowers the float sufficiently to close and open the associated switch. Such float switch devices require a number of moving parts which wear or bind and eventually fail; and the wearing and binding is often accelerated by the damp, corrosive and dirty environment in which these float switches are used. Failure of the switch can have catastrophic effects since when the pump does not operate the water accumulates and can flood the area. In the case of bilge pumps, the flooding can sink the vessel.
One attempt to eliminate the need for such float switches includes means to periodically, automatically, e.g. every five minutes, turn the pump on whether or not there is water or liquid buildup. The pump current is then monitored, and, if it is low, a no-load condition is detected and the pump is shut off. If the current is normal, a load condition is detected and the pump is permitted to keep pumping until the water is drained and the low current condition reoccurs. See U.S. Pat. No. 5,076,763, "Pump Control Responsive to Timer, Delay Circuit and Motor Current", by the present inventors. While this solves the float switch problems, it adds another. Namely, in some installations the noise of the pump turning on every five minutes or for a similar time interval annoys owners and crew. For, even if no water is present the pump still relentlessly makes noise every five minutes.